Typical fluid systems comprise a pump to move fluid and a regulator to maintain safe and desirable operating pressures. One particular application is a vacuum pump and regulator that form part of a fluid system to provide vacuum for milking cows.
In general, two basic types of fluid systems are used for providing the vacuum for milking cows. The first is a vacuum pump operated at a constant speed with a regulator that admits atmospheric air to limit and control the vacuum level of the system. This type of system provides excess capacity, resulting in wasted energy.
The second type of system has addressed the excess capacity problem by incorporating a variable speed motor and drive to limit the speed of the vacuum pump. This type of system relies on a pressure sensor to monitor the vacuum level and adjust the speed of the motor and vacuum pump to match the load requirements of the milking system. The disadvantage of this type of system is that the motor and vacuum pump speed must be monitored continuously and varied to provide adequate vacuum stability. This results, among other things, in additional mechanical wear on the vacuum pump and motor. Variation in the speed of the motor also produces undesirable voltage variations for the electrical power system and electromagnetic waves that can interfere with other electronic systems in use. The variation in speed also wastes electricity when the motor speed must be increased suddenly to meet the demands of a transient load condition.
In U.S. Pat. No. 5,141,403 issued to GUO et al., a low-energy-consuming apparatus and method for controlling vacuum levels in machine milking and other vacuum systems is illustrated wherein the apparatus comprises a low vacuum end and high vacuum reserve. The apparatus further comprises a first and second controller means. Upon sensing disturbances in the low vacuum end, the flow rate of air is adjusted to the high vacuum reserve. The vacuum in the milking system is maintained by air supplied to the pump substantially from the low vacuum end rather than from external air.
In U.S. Pat. No. 5,284,180 issued to GUO et al., a low-energy-consuming apparatus and method for controlling vacuum levels in machine milking and other vacuum systems is shown, comprising a first and second controller means. This apparatus performs essentially the same functions as the above-mentioned GUO et al. patent in substantially the same way.
In U.S. Pat. No. 5,613,514 issued to TAN et al., a pressure regulator apparatus and method for controlling the pressure in a pressure system is illustrated. A regulator control circuit compares the pressure measured to a predetermined set point value for maintaining pressure. The desired pressure is maintained by opening and closing a control valve by the regulator.
The present invention seeks to improve fluid pump systems. The invention reflects the discovery that a variable speed motor may be controlled by a controller with discrete speed settings to minimize energy and speed variations. The invention relies on an independent pressure regulator to provide the desired pressure operating level. Such a pressure regulator for a milking system admits atmospheric air to maintain the vacuum at a desired operating level. The pressure regulator reduces the admission of atmospheric air during transient conditions of increased system demand. The system operating level is monitored and the variable motor speed is adjusted to a predetermined, discrete speed setting, as required to provide adequate margin for the regulator to properly maintain the operating level, while limiting excess capacity to that required for occasional transient conditions.
The present invention has a self calibration feature that determines the discrete speed settings for a particular system. This is accomplished by placing the inventive controller in calibration mode, which results in the pump being operated initially at its maximum speed. The controller then determines the system operating pressure level and incrementally decreases the pump speed until the system operating pressure level begins to decrease. The minimum speed, as well as any desirable speed setting(s) between the minimum and the maximum, can be specified by the controller. The desired minimum speed can also be set independently. This feature is required for milking system vacuum pumps that have a minimum allowable operating speed.
The present invention can provide control for a variety of system configurations. Although the basic system is one in which a single pump is used, the invention can self calibrate and control multiple pumps, only one pump operating at a given time or more than one pump operating simultaneously.
The inventive design is not obvious from the teachings of the prior art. Numerous variable speed pump controllers have been designed that rely on the speed of the pump to provide adequate operating system pressure levels. The present invention minimizes energy consumption while also minimizing variations in pump speed.